The invention relates to automatic dishwasher detergents containing no phosphate builder salts.
Machine dishwashing is used in connection with practically all commercial and institutional dining facilities as well as in a rapidly increasing proportion of private homes. In commercial machines, the dishes to be washed are introduced into a zone where detergent solution is sprayed over them, the detergent solution being recycled and used repeatedly, and replenished intermittently. In home machines the detergent is used for only one load of dishes and is then discarded, although it, too, is recirculated during the washing operation. Hence in both types of machines, food soil concentrations in the wash solution of 0.05 to 0.1% or higher are considered to be moderate under average conditions.
It has been the practice in formulating machine dishwashing detergents to use primarily various combinations of inorganic sodium and potassium salts, such as polyphosphates, silicates, carbonates, and basic materials such as sodium and potassium hydroxides. It has not been possible to use effective amounts of well-known organic detergents such as the alkyl aryl sulfonates, alkyl sulfonates, alkanol amides, or alkyl aryl polyethers in spray-type mechanical dishwashing detergents because of the foam these materials develop during the washing operation. This foam causes overflow and loss of the wash solution, impairs the mechanical operation of the machine, and lowers the pressure at which the washing fluid is impelled against the utensils to be cleaned. The inorganic materials do not foam themselves, and, at low concentrations of food soil (less than 0.01%), perform satisfactorily in mechanical dishwashers. However, with an increase in food soil concentrations to greater than about 0.03%, foaming becomes a serious problem even with the use of purely inorganic detergent systems. This is because the inorganic detergent systems, being alkaline, can cause some saponification of fatty food soils. This, plus the natural foaming properties of protein food soils, tends to produce foam in the wash tank.
Current automatic dishwasher formulations contain from 10-60% phosphate salts, primarily in the form of polyphosphates and orthophosphates. The phosphates have been found to be highly effective soil removing agents, but are not without disadvantages. Phosphates and phosphate-containing detergent formulations have recently received considerable attention as prime suspects in water pollution. Phosphates are principally alleged to be causative in accelerated eutrification of the nation's waters, and there has recently been an increasing demand for effective detergent compositions which are low in phosphates or, preferably, entirely free of phosphates. With the increased growth of automatic dishwater sales (16% per annum), the demand for a phosphate-free automatic dishwashing composition is particularly great.